High temperature resistant gaskets are used to provide a seal against combustion gases at elevated temperatures. Such gaskets include cylinder head gaskets, exhaust manifold gaskets and turbocharger base gaskets. In particular, cylinder head gaskets typically extend around annular cylinder bores to provide a combustion seal, maintaining the high temperature gases of combustion within the cylinder bore. The gasket bears the load from a bolted connection of the engine block and cylinder head components and relies upon that load to provide a seal.
It is known to provide cylinder head gaskets with a single flange positioned adjacent a cylinder bore opening formed in a gasket body of the gasket. The flange is generally U-shaped in cross-section, having a central web portion separating upper and lower legs that extend continuously around an inner peripheral boundary of the cylinder bore opening and engage upper and lower surfaces of the gasket body. Typically, a sealing element such as a fire ring is disposed within a trough defined by the U-shaped cross-section of the flange to help protect the gasket body from the deleterious effects of the combustion environment.
Up to 30 percent of the clamping force from the bolted connection of the mechanical components is used to secure such flanges to the gasket body. Thus, this portion of the clamping force is not available to prevent leakage from the various seals. A high force is necessary due to the relatively large contact area between the mechanical components and the flange legs.
Moreover, U-shaped flanges are associated with high tooling and manufacturing costs. The sealing element must be manually loaded into the U-shaped trough. Then a closing die must be used that forms and presses the flange legs over the sealing element and the gasket body. A flattening operation is then required that must be inspected to confirm that the flange is at a pre-established height. Such operations restrict the construction of the U-shaped flanges to malleable metals.
The use of malleable metals in U-shaped flanges promotes flange thinning at flange/sealing element interfaces. Additionally, flange cracking may occur either during forming operations or in actual engine operation. U-shaped flanges are particularly susceptible to cracking in the central web portion between the upper and lower legs of the flange.
Further, by enclosing the sealing element within a U-shaped flange, the sealing element may not be visually inspected. Inspections using expensive electronic equipment have had only limited success.